<?php
// El APP ID de OfertoYa.com en facebook y el FACEBOOK SECRET
define('FACEBOOK_APP_ID', '289748777742997');
define('FACEBOOK_SECRET', '111658e15749ecbe149d8a1a317ce3ec');
// Funciones para decodificar el signed_request
function parse_signed_request($signed_request, $secret) {
  list($encoded_sig, $payload) = explode('.', $signed_request, 2); 

  // decode the data
  $sig = base64_url_decode($encoded_sig);
  $data = json_decode(base64_url_decode($payload), true);

  if (strtoupper($data['algorithm']) !== 'HMAC-SHA256') {
	error_log('Unknown algorithm. Expected HMAC-SHA256');
	return null;
  }

  // check sig
  $expected_sig = hash_hmac('sha256', $payload, $secret, $raw = true);
  if ($sig !== $expected_sig) {
	error_log('Bad Signed JSON signature!');
	return null;
  }

  return $data;
}

function base64_url_decode($input) {
	return base64_decode(strtr($input, '-_', '+/'));
}
?>